docs: def hdd_to_pmf(hypo_depth_dist, use_default=False):
      """
      Returns the hypocentral depth distribtuion as an instance of the :class:
      openquake.hazardlib.pmf. 
      """
      if isinstance(hypo_depth_dist, PMF):
          # Is already instance of PMF
          return hypo_depth_dist
      else:
          if use_default:
              # Default value of 10 km accepted
              return PMF([(1.0, 10.0)])
          else:
              # Out of options - raise error!
              raise ValueError('Hypocentral depth distribution not defined!')